The use of light to detect a pressure condition is known. In particular fiber optic cables and optical fibers have been used to detect pressure conditions.
In U.S. Pat. No. 4,845,357 (Brennan) back-scattered light arising within an optical fiber through the flexing of the fiber is detected. The fiber, operating in reflex mode, is embedded in a structure. The detected signal is used to activate piezo-electric elements attached elsewhere in the structure. See also U.S. Pat. No. 4,714,829 (Hartog et al) in a similar vein.
In U.S. Pat. No. 4,701,614 (Laeger) an optical fiber serves to sense pressure applied laterally to its side by the modulating effect that the deformation of the fiber wall has on the transmission of light within the fiber. See also U.S. Pat. No. 4,915,473 (Haese).
In U.S. Pat. No. 4,634,858 (Gerdt), an optical fiber coupling senses stress through variations in the index of refraction of a medium through which light is passed.
U.S. Pat. No. 5,425,273 (Chevalier) discloses a pressure sensor wherein an optical fiber terminates in a deformable, elastic and optically transparent material containing inclusions in the form of segments of optical fiber whose separating distances vary under applied pressure to modify the focal length of an optical system that reflects light back into the optical fiber.
A high pressure sensor based upon the optical detection of the deformation of a hollow glass sphere is described in an article: "A Novel Hollow--Glass Microsphere Sensor for Monitoring High Hydrostatic Pressure" by M. G. Xu and J. P. Dakin published in 2/SPIE Vol. 1795, Fiber Optic and Laser Sensors X (1992). The deformation under pressure of the sphere was detected by reflecting laser light supplied from an optic fiber off of the inner surfaces of the glass sphere. The reflected signals were analyzed in the manner of a Fabray-Perot interferometer for interference effects to sense deflections. No reliance upon scattered light occurs in this disclosure.
Sensors which rely upon reflected light to measure an external phenomon or influence that affects reflected or back-scattered light include:
(1) U.S. Pat. No. 4,599,908 (Sheridan)--pressure is sensed by constriction of compression-occluded holes located in the path of a reflected light beam; PA1 (2) U.S. Pat. No. 4,155,065 (Stimler)--a doppler laser particle motion detector is used to detect acoustic waves passing through a suspension of light scattering particles carried within a liquid; PA1 (3) U.S. Pat. No. 4,691,709 (Colien)--blood pressure at the distal end of a catheter, is sensed by the modulating effect of pressure on a flexible mirror presented before the end of an optical fiber light guide, operating in reflex mode; PA1 (4) U.S. Pat. No. 3,580,082 (Strack)--detects pressure by sensing the change in intensity of light reflected off of a deflecting membrane which directs light to alternate light sensing fibers; PA1 (5) U.S. Pat. No. 4,986,671 (Sun) relies upon an illuminating/receiving optical fiber operating in reflex mode to measure pressure applied to a deformable elastomeric material applied to the active end of optical fiber. Displacement of a reflective layer formed on the surface of the elastomeric material towards the optical fiber affects the level of optical coupling between the two modes in which the fiber is operating. This variation serves as a measure of the force or pressure applied at the fiber end; and PA1 (6) U.S. Pat. No. 4,870,271 (Philips)--a contacting sensor is based upon the reception of light reflected back from a deflecting, cantilevered spring. The spring is illuminated by light emitted from an optical fiber towards which the spring may deflect, and sensed by a paired optical fiber positioned adjacent to the illuminating fiber. PA1 "A hollow sphere, coated internally with a white diffusing material and provided with openings for incident beam, specimen, and detector, used for measuring the diffuse reflectance or transmittance of objects." PA1 (1) a compressible carrier medium of wave energy transmitting material having an outer boundary; PA1 (2) a wave energy source coupled to said carrier medium; PA1 (3) wave energy scattering centers dispersed within said carrier medium to create a scattered energy volume containing scattered wave energy; PA1 (4) a wave energy receiver responding to the integrated intensity of scattered wave energy within the scattered energy volume; and PA1 (5) signal coupling means connected to the wave energy receiver for transferring signals therefrom to a pressure indicator, PA1 (1) a source of illumination; PA1 (2) a compressible light scattering medium or hollow, compressible structure defining an integrating cavity within which light from the source of illumination is diffused and integrated through multiple scattering; PA1 (3) a light sensing means directed in a viewing direction to sample diffused and integrated light arising from multiple scattering within the integrating cavity and provide a signal indicative of the intensity of the diffused and integrated light; and PA1 (4) signal coupling means connected to the light sensing means for transferring the signal to a pressure indicator, PA1 structurally self-supporting PA1 compressible i.e. volumetrically compactable PA1 elastically resilient (optional) PA1 at least partially transmissive of light, e.g.--translucent PA1 scattering centers which change density upon compression of the medium
The Philips, Sun and other patents describe pressure sensing systems in which a pressure-induced deflection of a resilient member towards a light sensor is detected by the change in brightness of an illuminated surface. The sensor viewing the illuminated surface in these references is oriented towards the deflecting surface and the source of applied pressure. This limits the mechanical configuration of the combined pressure sensing system. In particular, Philips and Sun do not provide a means for detecting pressure applied obliquely or laterally to the viewing orientation of the light sensor.
Further, none of these references rely upon the change in the integrated intensity of multiply scattered wave energy, e.g. light, present within a volume which is akin to an "integrating cavity", or "integrating optical cavity" as the volume of such cavity is varied. ("Multiply" is used herein in its adverb sense.)
An integrating cavity or volume as used herein is similar to in certain aspects to an "Integrating Sphere". An Integrated Sphere is defined in The Photonics Dictionary 1997--Publisher Laurin Publishing Co. Inc., Pittsfield, Mass. at page D-72 as:
The light within such a volume is repeatedly scattered to such an extent that it is locally nearly isotropic in character, i.e. its intensity at a point is virtually the same when measured in all directions. Such a sphere is used to measure the total quantity of light emitted from a source.
The effect of pressure on a compressible, light scattering medium or volume that is volumetrically compactable and which contains scattered light or wave energy has not been exploited in any publicized devices. An opportunity exists to create a pressure sensing device and system which is capable of providing, at reasonable cost, a measure of applied pressure, both locally and over a specific surface area, relying upon the detection of scattered light or wave energy. The invention herein addresses those objects.
Prior art designs tend to be limited by the necessity of viewing a pressure responding surface that is displaced axially towards a sensor. This limits the use of such configurations because they are insensitive, or are relatively insensitive, to laterally-applied pressure. By providing a sensor arrangement that is sensitive to laterally-applied pressure it becomes possible to construct an array that provides a pressure sensitive surface of substantial area and minimal thickness at relatively low cost. This is, therefore, a further object of the present invention.
The invention in its general form will first be described, and then its implementation in terms of specific embodiments will be detailed with reference to the drawings following hereafter. These embodiments are intended to demonstrate the principle of the invention, and the manner of its implementation. The invention in its broadest and more specific forms will then be further described, and defined, in each of the individual claims which conclude this Specification.